The knots need to withstand significantly greater forces than that. The force that the knots need to handle depends primarily on (assuming the weight in the hammock is constant) the angle between the horizontal plane and the lowest point of the hammock when lying in it.
Example: If the hammock hangs so that the line between the bottom and the attachment point is 10 degrees, the resulting force on the attachment point is just over 10000 N, 1 ton! If you hang it so that it sags more in the middle and the angle is instead 20 degrees, the force on the attachment is only 6000 N, 600 kg. This is the force PER attachment.
There can therefore be significant forces involved if you hang the hammock flat, and if you also take into account dynamic forces (swinging, movements up and down), they can become even greater. So, what you attach the hammock to is very important. Whether it will work in your case, I can't say; someone more knowledgeable in home construction would need to determine that...
/Kalle